Electrical device



April 1950 R. B. MANNING 2,502,970

suzcmxcm. DEVICE Filed Oct. 11, 1946 INVE/V TOR R. 8. MA NN/NG Patented Apr. 4, 1950 ELECTRICAL DEVICE Robert B. Manning, Westfleld, N. J., assignor to Western Electric Com 1 York, N. Y., a corner pany, Incorporated, New ation of New York Application October 11, 1946, Serial No. 702,709

This invention relates to an electrical device,

and more particularly to a metal coated crystal having a metal terminal wire secured thereto.

There are numberless uses in the electrical arts for a thin slab of dielectric crystalline material, commonly called a crystal in those arts, having a closely adherent coating of metal on one or both large faces and having a terminal wire or rod secured to be mechanically rigid with the crystal and electrically connected to a metal coating thereon. Such crystals have usually been made from hard and toughly durable natural mineral crystals, e. g., quartz par excellence. However, the supply of suitable natural material is insufiicient to meet the demand, and crystals artificially grown from various soluble compounds which crystallize without water of crystallization and therefore are not, in general, eillorescent, are being used to supplement the materials obtainable from natural sources. Compounds such as ammonium dihydrogen phosphate, potassium dihydrogen phosphate and others are found to be satisfactory for such use. Crystalline material so derived does not have the mechanical strength nor the hardness nor the resistance to destruction by heat exhibited by crystalline silica in natural quartz. Methods and arrangements satisfactorily suitable for securing terminal wires to quartz crystals (crystal, without quotes, will hereinafter mean the slabs of the art) are often found to be impracticable for the far less rugged artificial crystals.

A prime object of the present invention is to provide a structure for the assembly of a crystal, a coating thereon, and a terminal therefor which shall be simple to make without breakage or failure and reliably durable in operation.

With the above and other objects in view the invention may be embodied in a crystal structure comprising a body of crystalline dielectri material having a smooth face thereon, a terminal base member having a corresponding face thereon, and apposed against the said face of the crystal, and a layer of thermoplastic adhesive material interposed between the apposed faces and securing the terminal base to the crystalline body, and consisting of more than 85% of a synthetic thermoplastic resin and less than 15% of a synthetic thermosetting resin.

Other objects and features of the invention will appear from the following detailed description of an illustrative embodiment thereof, taken in connection with the accompanying drawing in which the single figure is a very much enlarged view in central vertical longitudinal section of a portion 3 Claims. (Cl. 171-327) of a crystal constructed in accordance with the invention.

The, illustrative embodiment of the invention herein disclosed comprises a thin, flat slab I0 of suitable crystalline material having a smooth upper face upon which rests a terminal base member l2 of suitable metal in the form of a lamella or small plate of sheet metal, here shown as a circular disk, but which may be of any desired peripheral contour so long as its under face is smooth and conforms to the upper face of the slab Ill. The base I2 is mechanically secured to the slab II] by an intercalated layer ll of suitable thermoplastic cement, the thermoplastic character of this cement being the characterizing, crucial feature of the present invention. A terminal wire or rod H is secured rigidly to the base 12, e. g., by welding as indicated at l3, by soldering, or by having been made originally integral therewith. And, finally, a metal coating l 5 extends over the upper surface of the slab l0 and over the exposed sides and top of the base I2.

While the invention is applicable in the case of crystals of natural quartz, it finds its use primarily when the slab I0 is of less rugged crystalline substance such as the artificially grown crystalline materials mentioned above. The coating I5 may preferably be of silver, but may be of any metal desired in particular cases. Similarly, the terminal II and terminal base l2 may be of any material suitable for the purpose in hand. The specific composition or character of none of these elements is material to the invention.

The case of the adhesive layer I, however, is different. Here the nature and composition of the substance are crucially material to and characteristic of the invention. It has been found that, for satisfactory assembly of the parts as shown, the substance of the adhesive layer ll must be a composition comprising mainly a thermosplastic synthetic resin, preferably polymerized vinyl acetate, to which has been added a small proportion of thermosetting synthetic resin, e. g., the phenol-formaldehyde condensation product familiarly known as Bakelite. The admixture of thermosetting resin must be sufficiently small in proportion to ensure that the thermoplastic character of the composition is not destroyed, and sufficiently large to raise the softening temperature of the compound to a value practicable for the intended use of the finished device.

Copending application Serial No. 684,257, flied July 7, 1946, now U. S. Patent No. 2,468,594, by the present inventor together with another, dis- 3 closes and specifically claims a composition applicable to the present use. The cement therein described is broadly Parts by weight Methyl acetate solvent 38 to 50 Vinyl acetate polymer 12 to 19 Phenol-formaldehyde resin 0.2 to 2.0 Mica flour to 45 For present purposes the mica flour will, in most instances, be reduced materially or even entirely omitted. Thus, where the layer It is desired to be 01' minimum thickness, a preferred composition for the cement without any filler may be:

Parts by weight Methyl acetate solvent 38 to 50 Vinyl acetate polymer 12 to 19 Phenol-formaldehyde resin 0.2 to 2.0

For the particular case where the slab I9 has a frostily smooth surface and the disk I! is of beryllium copper alloy, the preferred composition of the cement is one containing no filler follows:

III

' Parts by weight Methyl acetate solvent About 43 Vinyl acetate polymer About 17 Phenol-formaldehyde resin About 1.2

Per cent by weight 2. Vinyl acetate polymer 85 to 99 Phenol-formaldehyde resin 15to 1 3. Vinyl acetate polymer About 94 Phenol-formaldehyde resin About 6 What is claimed is: 1. In an electrical crystal device having a member of crystalline material and a terminal base member of metal having mounted thereon a metal wire, the combination with the said members of adhesive material between the said members to hold the same together and consisting of or more of a synthetic thermoplastic resin and a quantity of a synthetic thermosetting resin not exceeding 15%.

2. In an electrical crystal device having a member of crystalline material and a terminal base member of metal having mounted thereon a metal wire, the combination with the said members of adhesive material between the said members to hold the same together and consisting of Per cent Vinyl acetate polymer resin 85 to 99 Phenol-formaldehyde resin 15to l 3. In an electrical crystal device having a member of crystalline material and a terminal base member of metal having mounted thereon a metal wire. the combination with the said members of adhesive material between the said members to hold'the same together and consisting of Per cent Vinyl acetate polymer resin About 94 Phenol-formaldehyde resin About 6 ROBERT B. MANNING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

